1. Field
The present invention relates to a manufacturing method and an apparatus for a fiber reinforced polymer (FRP) bar, and more particularly, to a manufacturing method and an apparatus for a FRP bar which does not cause excessive bending deflection even though a fiber having a low elastic modulus is used, by introducing a compression force in advance. In addition, the present invention relates to a method and an apparatus for manufacturing a hybrid FRP bar by using at least two kinds of fibers so that the fibers may be easily distributed to specific locations at the section of the manufactured hybrid FRP bar, and a nozzle for such an apparatus.
2. Description of the Related Art
A steel bar used for a reinforced concrete structure is always exposed to possibility of corrosion. A steel bar in concrete is highly likely to contact moisture due to cracks or the like, and in particular, the steel bar is corroded due to residual moisture in the concrete, in addition to cracks. If the steel bar is corroded, the volume of the steel bar expands, which results in separation of concrete cover. Therefore, the reinforced concrete structure loses integrity, which is an essential requirement of the reinforced concrete structure, and is not able to serve as a structural member.
In order to solve this problem, rod-shaped products manufactured using a fiber reinforced polymer (FRP) have been used instead of steel bars distributed in a concrete structure or to assist the steel bars. Such a rod-shaped product manufactured using FRP is generally called “FRP bar” or “FRP re-bar” since it is used for reinforcing a concrete structure.
Korean Patent Registration No. 10-0702629 discloses a technique for manufacturing such a FRP bar, and FIG. 1 shows a schematic configuration of an existing device for manufacturing a FRP bar. As shown in FIG. 1, in an existing technique, a FRP bar 1 is manufactured by a manufacturing apparatus including a fiber winding reel 101, a resin supplier 102, a nozzle 100, a heater 104 and a drawer 105. In order to manufacture the FRP bar, first, fibers as thin as threads, supplied from the fiber winding reel 101, are bound into a bundle and drawn to the drawer 105. In this time, while passing through the resin supplier 102, the fibers are formed into a rod shape while entering the nozzle 100 together with a resin, and the resin is hardened through the heater 104, thereby making the FRP bar 1.
The fibers used for manufacturing a rod-shaped FRP bar 1 having a circular, oval or polygonal section by bundling the fibers impregnated in a resin as described above use carbon fibers, aramid fibers, steel wires, glass fibers or the like, among which glass fibers are advantageous for cost reduction. However, when the FRP bar 1 is manufactured using glass fibers, the glass fibers have a lower elastic modulus than the steel bar even though its tensile strength is much greater than that of the steel bar. Therefore, if the FRP bar 1 is used for reinforcing a bending member, a great drooping is caused at the bending member. In other words, if the FRP bar 1 is manufactured using a fiber having a low elastic modulus such as a glass fiber, an excessive bending deflection is caused at a concrete structure to which a bending load is applied.
As a solution, there has been proposed a technique for manufacturing a FRP bar by mixing several kinds of fibers having different elastic modulus. The FRP bar 1 manufactured using several kinds of fibers together may be called a “hybrid FRP bar”. The hybrid FRP bar may ensure good economical feasibility since several kinds of fibers are mixed, thereby ensuring more improved elastic modulus in comparison to a FRP using only glass fibers. The hybrid FRP bar may use, for example, a glass fiber having a low elastic modulus and a carbon fiber having a high elastic modulus.
However, when manufacturing a hybrid FRP bar by using several kinds of fibers, it may be needed to distribute the several kinds of fibers at different locations in the section of the FRP bar. If the hybrid FRP bar uses a glass fiber and a carbon fiber as in the above example, it may be needed to locate the glass fiber at the center of the section and the carbon fiber at the periphery of the section.
Fibers used in the FRP bar have a very small diameter like threads and several ten or hundred strands are bundled. However, there has not been developed a technique for efficiently manufacturing a hybrid FRP bar using several kinds of fibers which are distributed at specific locations in the section of the FRP bar as designed.